A 45-year-old man presents to the emergency department with fever, tachycardia and hypotension thought to be due to pneumonia. His blood pressure is 80/50 mm Hg, heart rate 122 beats/min, respiratory rate 28 breaths/min and lactate 4.2 mmol/L. According to the 2021 Surviving Sepsis Campaign, which initial management step is most appropriate within the first 3 hours?